Coil-on-plug ignition - secondary vs primary voltage and current

You will require a PicoScope to perform this test. A list of suitable accessories can be found at the bottom of this page.

Note: This helpfile refers to a 20:1 attenuator. If you are using a 10:1 attenuator please adjust the Probe settings for the relevant channel. These settings can be found under the Channel Options button, then: Probe > 10:1 Attenuator.

How to perform the test

Channel A: Primary voltage

Plug the 20:1 Attenuator into Channel A on the PicoScope and plug a BNC test lead into the attenuator. Fit a large black clip onto the black test connector (earth) and a back-pinning probe on the coloured connector (positive). Place the black clip on the battery negative terminal and probe the coil's negative (or number 1) terminal with the back-pinning probe.

Channel B: Secondary voltage with COP probe

Using the COP Probe cable with ground clip (TA033) connect the end with the ground clip to the scope's Channel B input and the other end to the COP Probe. Connect the ground clip to a reliable ground point on the engine block.

When placing the tip of the probe on the coil, ensure that you use the flat edge. Try to be consistent with the position on the coil: find the best signal on the first coil to be tested and then repeat that on the other coils.

Channel C: Primary current

Connect the low-amp current clamp to Channel C of the PicoScope. Select the 20 A rangeif applicable and switch the current clamp on. Rremember to zero the clamp before connecting it to the circuit.

The current clamp should be placed directly onto the coil's supply cable and not around the loom that also contains the negative (or negatives depending on the ignition system). The connection is illustrated in Figure 1.

Example waveform

Waveform notes

This test produces the three waveforms shown above. Similar waveforms are discussed in the following topics:

Channel A (middle, blue): Primary voltage

Channel B (bottom, red): Secondary voltage with COP probe

Channel C (top, green): Primary current

AT079-4

Disclaimer
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.